Biphasic effect of cell surface sialic acids on pancreatic cancer cell adhesiveness

Altered glycosylation in pancreatic cancer and beyond

Pancreatic ductal adenocarcinoma (PDA) is one of the deadliest cancers and is projected to soon be the second leading cause of cancer death. Median survival of PDA patients is 6-10 mo, with the majority of diagnoses occurring at later, metastatic stages that are refractory to treatment and accompanied by worsening prognoses. Glycosylation is one of the most common types of post-translational modifications. The complex landscape of glycosylation produces an extensive repertoire of glycan moieties, glycoproteins, and glycolipids, thus adding a dynamic and tunable level of intra- and intercellular signaling regulation. Aberrant glycosylation is a feature of cancer progression and influences a broad range of signaling pathways to promote disease onset and progression. However, despite being so common, the functional consequences of altered glycosylation and their potential as therapeutic targets remain poorly understood and vastly understudied in the context of PDA. In this review, the functionality of glycans as they contribute to hallmarks of PDA are highlighted as active regulators of disease onset, tumor progression, metastatic capability, therapeutic resistance, and remodeling of the tumor immune microenvironment. A deeper understanding of the functional consequences of altered glycosylation will facilitate future hypothesis-driven studies and identify novel therapeutic strategies in PDA.

Lysosomes and Cancer Progression: A Malignant Liaison

During primary tumorigenesis isolated cancer cells may undergo genetic or epigenetic changes that render them responsive to additional intrinsic or extrinsic cues, so that they enter a transitional state and eventually acquire an aggressive, metastatic phenotype. Among these changes is the alteration of the cell metabolic/catabolic machinery that creates the most permissive conditions for invasion, dissemination, and survival. The lysosomal system has emerged as a crucial player in this malignant transformation, making this system a potential therapeutic target in cancer. By virtue of their ubiquitous distribution in mammalian cells, their multifaced activities that control catabolic and anabolic processes, and their interplay with other organelles and the plasma membrane (PM), lysosomes function as platforms for inter- and intracellular communication. This is due to their capacity to adapt and sense nutrient availability, to spatially segregate specific functions depending on their position, to fuse with other compartments and with the PM, and to engage in membrane contact sites (MCS) with other organelles. Here we review the latest advances in our understanding of the role of the lysosomal system in cancer progression. We focus on how changes in lysosomal nutrient sensing, as well as lysosomal positioning, exocytosis, and fusion perturb the communication between tumor cells themselves and between tumor cells and their microenvironment. Finally, we describe the potential impact of MCS between lysosomes and other organelles in propelling cancer growth and spread.

Insight in Adhesion Protein Sialylation and Microgravity Dependent Cell Adhesion-An Omics Network Approach

The adhesion behavior of human tissue cells changes in vitro, when gravity forces affecting these cells are modified. To understand the mechanisms underlying these changes, proteins involved in cell-cell or cell-extracellular matrix adhesion, their expression, accumulation, localization, and posttranslational modification (PTM) regarding changes during exposure to microgravity were investigated. As the sialylation of adhesion proteins is influencing cell adhesion on Earth in vitro and in vivo, we analyzed the sialylation of cell adhesion molecules detected by omics studies on cells, which change their adhesion behavior when exposed to microgravity. Using a knowledge graph created from experimental omics data and semantic searches across several reference databases, we studied the sialylation of adhesion proteins glycosylated at their extracellular domains with regards to its sensitivity to microgravity. This way, experimental omics data networked with the current knowledge about the binding of sialic acids to cell adhesion proteins, its regulation, and interactions in between those proteins provided insights into the mechanisms behind our experimental findings, suggesting that balancing the sialylation against the de-sialylation of the terminal ends of the adhesion proteins' glycans influences their binding activity. This sheds light on the transition from two- to three-dimensional growth observed in microgravity, mirroring cell migration and cancer metastasis in vivo.

The metastasis-inducing protein AGR2 is O-glycosylated upon secretion from mammary epithelial cells

AGR2 is overexpressed in multiple cancers, particularly those arising from breast and prostate tissues, and higher levels of AGR2 are associated with earlier patient death. Although AGR2 is normally resident within the endoplasmic reticulum, the protein has been found in the extracellular space in several model systems. However, it has never been expressly demonstrated that this extracellular form of the protein is secreted and does not just accumulate in the extracellular space as a result of cell lysis. We show in this paper that AGR2 protein is secreted by both human and rat mammary epithelial cells in culture. Furthermore, this secreted form of AGR2 becomes O-glycosylated, with no detectable presence of N-glycosylation. Importantly, this post-translationally modified AGR2 is only detected in the conditioned medium from non-leaky cells, suggesting that membrane integrity must be maintained to allow AGR2 glycosylation. The results suggest a possible role for O-glycosylation in modulating the extracellular functions of AGR2.

Mucins in pancreatic cancer and its microenvironment

Pancreatic cancer remains a lethal malignancy with poor prognosis owing to therapeutic resistance, frequent recurrence and the absence of treatment strategies that specifically target the tumour and its supporting stroma. Deregulated cell-surface proteins drive neoplastic transformations and are envisioned to mediate crosstalk between the tumour and its microenvironment. Emerging studies have elaborated on the role of mucins in diverse biological functions, including enhanced tumorigenicity, invasiveness, metastasis and drug resistance through their characteristic O-linked and N-linked oligosaccharides (glycans), extended structures and unique domains. Multiple mucin domains differentially interact and regulate different components of the tumour microenvironment. This Review discusses: the expression pattern of various mucins in the pancreas under healthy, inflammatory, and cancerous conditions; the context-dependent attributes of mucins that differ under healthy and pathological conditions; the contribution of the tumour microenvironment in pancreatic cancer development and/or progression; diagnostic and/or prognostic efficacy of mucins; and mucin-based therapeutic strategies. Overall, this information should help to delineate the intricacies of pancreatic cancer by exploring the family of mucins, which, through various mechanisms in both tumour cells and the microenvironment, worsen disease outcome.

Altered expression of sialylated glycoproteins in ovarian cancer sera using lectin-based ELISA assay and quantitative glycoproteomics analysis

Herein, we identify and confirm differentially expressed sialoglycoproteins in the serum of patients with ovarian cancer. On the basis of Sambucus nigra (SNA) lectin enrichment and on an isobaric chemical labeling quantitative strategy, clusterin (CLUS), leucine-rich alpha-2-glycoprotein (LRG1), hemopexin (HEMO), vitamin D-binding protein (VDB), and complement factor H (CFH) were found to be differentially expressed in the serum of patients with ovarian cancer compared to benign diseases. The abnormal sialylation levels of CLUS, CFH, and HEMO in serum of ovarian cancer patients were verified by a lectin-based ELISA assay. ELISA assays were further applied to measure total protein level changes of these glycoproteins. Protein levels of CLUS were found to be down-regulated in the serum of ovarian cancer patients, while protein levels of LRG1 were increased. The combination of CLUS and LRG1 (AUC = 0.837) showed improved performance for distinguishing stage III ovarian cancer from benign diseases compared to CA125 alone (AUC = 0.811). In differentiating early stage ovarian cancer from benign diseases or healthy controls, LRG1 showed comparable performance to CA125. An independent sample set was further used to confirm the ability of these candidate markers to detect patients with ovarian cancer. Our study provides a comprehensive strategy for the identification of candidate biomarkers that show the potential for diagnosis of ovarian cancer. Further studies using a large number of samples are necessary to validate the utility of this panel of proteins.

Altered expression of sialylated glycoproteins in breast cancer using hydrazide chemistry and mass spectrometry

Sialylation is one of the altered protein glycosylations associated with cancer development. The sialoglycoproteins in cancer cells, however, largely remain unidentified because of the lack of a method for quantitative analysis of sialoglycoproteins. This manuscript presents a high throughput method for quantitative analysis of N-linked sialoglycoproteins using conditional hydrazide chemistry, liquid chromatography, and tandem mass spectrometry. We further applied the sialoglycoproteomic method to the profiling of breast cancer tissues and compared findings with the results from the total glycoproteomic analysis using the original hydrazide chemistry method. We identified altered expression of sialoglycoproteins, as well as the total glycoprotein changes associated with breast cancer. Using lectin and Western blot analysis, we characterized one of the sialoglycoproteins, versican, and confirmed that versican was most sialylated and elevated in breast cancer. Furthermore, we showed that versican was detected in both cancer epithelial cells and peritumoral stromal cells using immunohistochemistry. Tissue microarray analysis revealed that epithelial expression of versican had significant relations to lymph node metastasis and pathological stages. This is the first quantitative sialoglycoproteomic and glycoproteomic analysis of breast cancer and noncancerous tissues. These findings present a significant addition of the method to the identification of altered expression of sialylated glycoproteins associated with breast cancer development.

Sialilated β1,6 branched N-oligosaccharides modulate adhesion, chemotaxis and motility of melanoma cells: Effect on invasion and spontaneous metastasis properties

B16BL6 cells, selected specifically for invasive characteristics from B16F10 mouse melanoma cells, displayed greater ability to metastasize to lungs and produced larger colonies than the parent cells, when injected intravenously. When the two cell lines were compared for surface beta1,6-branched N-oligosaccharides by flow cytometry using Leuco-Phyto-Heam-Agglutinin, B16BL6 were found to express significantly higher levels. Inhibition of the oligosaccharide expression, by treatment of the cells with swainsonine or antisense-N-acetyl glucosaminyl-transferase-V, significantly reduced metastasis and invasion (>50%). Further, inhibition of oligosaccharides on the molecules like beta1 integrin (one of the major carriers) caused 30-45% reduction in their adherence to extra-cellular-matrix components especially collagen IV and laminin, and chemotaxis towards fibronectin and matrigel. The inhibition also decreased haptotaxis by approximately 50% to fibronectin but surprisingly was enhanced towards laminin by approximately 75%. The cells on which the expression of these oligosaccharides was inhibited failed to exhibit the characteristic spontaneous metastasis and adhesion properties of B16BL6 cells. In none of the cases, however, the secretion of matrix-metallo-proteases correlated with oligosaccharide expression. Sialylation of surface oligosaccharides was found to be accompanied by even higher motility and adherence to the substrates. These results strongly support an important role of cell surface beta1,6-linked N-oligosaccharides, especially the sialylated derivatives, in the processes that influence invasion and metastasis.

Newcastle disease virus neuraminidase primes neutrophils for stimulation by galectin-3 and formyl-Met-Leu-Phe

Human neutrophils are activated by the beta-galactoside-binding lectin galectin-3, provided that the cells are primed by in vivo extravasation or by in vitro preactivation with, for example, LPS. Removal of terminal sialic acid can change neutrophil functionality and responsiveness due to exposure of underlying glycoconjugate receptors or change in surface charge. Here, we investigated whether such alteration of the cell surface carbohydrate composition can alter the responsiveness of the cells to galectin-3. Neutrophils were treated with neuraminidases (NA) of different origins: Clostridium perfringens (CP), Salmonella typhimurium, Vibrio cholerae, and Newcastle disease virus (NDV). In the presence of NDV-NA, but no other NA, the otherwise non-responding neutrophils responded readily to galectin-3 by activation of the NADPH-oxidase. The galectin-3 priming effect was inhibited by the sialidase inhibitor 2,3-dehydro-2-deoxy-N-acetyl-neuraminic acid. Earlier studies have shown that priming of the neutrophil response to galectin-3 with, for example, LPS is paralleled by degranulation of intracellular vesicles and granules and upregulation of potential galectin-3 receptors. Also, NDV-NA (but not CP-NA) treatment induced degranulation, shown as an upregulation of complement receptor 3. Since not only the galectin response but also the response to the chemoattractant fMLF was primed, NDV-NA appears to induce a general priming phenomenon, possibly due to receptor upregulation by degranulation.

Cholangiocarcinoma: recent progress. Part 2: molecular pathology and treatment

Part 2 of this review discusses DNA damage in biliary epithelial cells in the development of cholangiocarcinoma, alterations in cell kinetics of biliary epithelial cells, biliary epithelial mitoinhibition, and apoptosis that includes the role of Bcl-2, transforming growth factor-beta, telomerase activities and deregulation of Ras and p53, cancer-associated antigens in cholangiocarcinoma, precancerous lesions, stroma formation and angiogenesis, cancer invasion, cell-cell and cell-matrix interactions, and the mechanism of evasion from immune surveillance. These discussions are followed briefly by treatments such as photodynamic therapy, and surgical approaches comparing resection and liver transplantation.

Mucinous (colloid) adenocarcinomas secrete distinct O-acylated forms of sialomucins: a histochemical study of gastric, colorectal and breast adenocarcinomas

AIMS

Mucinous (colloid) adenocarcinomas represent a distinct group of tumours defined by the presence of large amounts of extracellular mucins. By using histochemical methods, we analysed mucins secreted by mucinous versus non-mucinous adenocarcinomas and looked for differential secretion profiles.

METHODS AND RESULTS

Sixty-four adenocarcinomas were studied (23 colorectal, 17 gastric, and 24 breast tumours). Thirty-two tumours were of the colloid type. The following methods were applied to paraffin tissue sections: (i) Alcian blue (pH 2.5) and periodic acid-Schiff (PAS); (ii) high iron diamine and Alcian blue (pH 2.5); (iii) periodic acid borohydride, potassium hydroxide, and PAS; (iv) periodic acid-thionine Schiff, potassium hydroxide, and PAS; and (v) periodic acid-borohydride and PAS. Most adenocarcinomas secreted acidic mucins, with sialomucins predominating over sulfomucins, except for non-mucinous adenocarcinomas of the breast which showed predominant neutral mucins. All mucinous adenocarcinomas contained C9-O-acyl sialic acid as mono, di(C8,C9)-, or tri(C7,C8,C9)-O-acyl forms. Acidic mucins secreted by the majority of non-colloid adenocarcinomas consisted of non-O-acylated sialomucins.

CONCLUSIONS

C9-O-acylation of sialic acid is a characteristic feature of mucinous adenocarcinomas and can be readily detected by histochemical methods.

A novel orthotopic implantation model of human esophageal carcinoma in nude rats: CD44H mediates cancer cell invasion in vitro and in vivo

A new orthotopic esophageal cancer model was developed by implanting fragments of xenografts of T.T human esophageal squamous carcinoma cells into the cervical esophagus of athymic rats. The rats had symptoms analogous to the human clinical course such as respiratory distress, dysphagia, vomiting of blood, or Horner syndrome, followed by death resulting from suffocation. Microscopic metastases of lymph node were observed around the tumor in 3 of 18 rats. A new cell line (T.T-1) was established from these metastases. Flow cytometry showed that T.T-1 and T.T parental cells had nearly the same surface levels of beta1-integrin, alpha2-integrin, alpha3-integrin and E-cadherin, and no expression of CD44v3, CD44v6 and alpha5-integrin. T.T-1 cells had a higher level of CD44H, however, and a greater binding efficiency to the extracellular matrix components; laminin, type IV collagen, hyaluronic acid, and fibronectin than T.T cells. Anti-CD44H antibody significantly decreased the binding efficiency of T.T-1 cells. T.T-1 cells were also significantly more invasive than T.T cells through all the extracellular matrix components except hyaluronic acid. After orthotopic implantation histological examination showed that T.T-1 tumors invaded beyond the esophageal mucosa and tracheal muscle layer and obstructed the esophagus and trachea. No invasion was observed with T.T tumors. Rats with T.T-1 or T.T tumors survived an average of 32.0 and 50.7 days, respectively (p < 0.01). In addition T.T-1 tumors expressed higher levels of CD44H mRNA than T.T tumors. In summary, our newly developed orthotopic implantation model is a valid model of esophageal cancer because it followed the same clinical course experienced by humans. Moreover, using cells derived from this model, we were able to demonstrate that CD44H is involved in esophageal cancer cell invasion.

Regulation of renal epithelial cell affinity for calcium oxalate monohydrate crystals

The binding and internalization of calcium oxalate monohydrate (COM) crystals by tubular epithelial cells may be a critical step leading to kidney stone formation. Exposure of MDCK cells to arachidonic acid (AA) for 3 days, but not oleic or linoleic acid, decreased COM crystal adhesion by 55%. Exogenous prostaglandin PGE(1) or PGE(2) decreased crystal binding 96% within 8 h, as did other agents that raise intracellular cAMP. Actinomycin D, cycloheximide, or tunicamycin each blocked the action of PGE(2), suggesting that gene transcription, protein synthesis, and N-glycosylation were required. Blockade of crystal binding by AA was not prevented by the cyclooxygenase inhibitor flurbiprofen, and was mimicked by the nonmetabolizable AA analog eicosatetryanoic acid (ETYA), suggesting that generation of PGE from AA is not the pathway by which AA exerts its effect. These studies provide new evidence that binding of COM crystals to renal cells is regulated by physiological signals that could modify exposure of cell surface molecules to which the crystals bind. Intrarenal AA, PGs, and/or other agents that raise the intracellular concentration of cAMP may serve a protective function by preventing crystal adhesion along the nephron, thereby defending the kidney against crystal retention and stone formation.

Expression of MUC1 and MUC2 mucin antigens in intrahepatic bile duct tumors: its relationship with a new morphological classification of cholangiocarcinoma

Our previous immunohistochemical study on intrahepatic bile duct tumors showed that invasive cholangiocarcinoma (ICC) with a poor outcome expressed MUC1 mucin but was negative for MUC2 mucin, whereas bile duct cystadenocarcinoma (BDCC) with a favorable outcome was MUC1 negative and MUC2 positive. In the present study, ICC was further subdivided into 2 subtypes: intraductal growth type and/or periductal infiltrating type (ICC-IP) and mass forming type (ICC-M). The survival of patients with BDCC or ICC-IP is significantly better than that of patients with ICC-M. We examined these subtypes (ICC-IP and ICC-M) and BDCC for their expression of MUC1 mucins of different glycoforms. ICC-M showed significantly higher MUC1 expression rates (90%, 95%, and 85% positive rates as measured with the DF3, MY.1E12, and MUC1-Glycoprotein antibodies, respectively) than BDCC and ICC-IP (14% and 33%, 58% and 58%, and 0% and 50% positive respectively, as measured by the same antibodies). In contrast, BDCC (86% positive) and ICC-IP (67% positive) showed significantly higher MUC2 expression rates than ICC-M (25% positive) as measured with the anti-MRP antibody. Thus, the immunohistochemical staining pattern of ICC-IP resembled the pattern of BDCC more than they resembled ICC-M. In general, MUC1 expression is associated with poor patient outcome, irrespective of the glycosylation status. In particular, high expression of more sialylated forms of MUC1 mucins was correlated with poor survival. In contrast, expression of non-sialylated MUC2 mucin is a favorable prognostic indicator. These results suggest that ICC-IP is a different entity from ICC-M. This reclassification may have value in determining prognosis and treatment method.

Altered expression of sialylated carbohydrate antigens in HT29 colonic carcinoma cells

To determine whether cell growth conditions impacted carbohydrate expression, HT29 cells were gradually transferred from a conventional glucose-containing media to a glucose-free galactose containing media. Indirect immunofluorescence on acetone fixed cells showed increased expression of sialyl Lewis A antigen (CA19-9), sialyl Lewis C (DUPAN2) and Tn/sialyl-Tn on the surface of HT29 cells grown in the glucose-free galactose containing media compared to those grown in the glucose containing media. Sialyltransferases responsible for the synthesis for these sialylated epitopes were Increased in the galactose-fed HT29 cells. Media overlying the cells was subjected to isopycnic ultracentrifugation in cesium chloride and the fractions derived from both glucose and galactose media with equivalent buoyant densities of 1.56 g/L, which are predicted to contain mucin glycoforms, were further separated by HPLC using a Mono-Q anion exchange column. The chromatograph of eluent from the sample derived from the cells growing in the galactose containing media showed an increased peak that reacted with the anti-sialyl Lewis A antibody, CA19-9. These results show that alteration of in vitro culture conditions may cause HT29 colonic carcinoma cells to alter the expression of sialylated carbohydrates.

Concepts and principles of O-linked glycosylation

The biosynthesis, structures, and functions of O-glycosylation, as a complex posttranslational event, is reviewed and compared for the various types of O-glycans. Mucin-type O-glycosylation is initiated by tissue-specific addition of a GalNAc-residue to a serine or a threonine of the fully folded protein. This event is dependent on the primary, secondary, and tertiary structure of the glycoprotein. Further elongation and termination by specific transferases is highly regulated. We also describe some of the physical and biological properties that O-glycosylation confers on the protein to which the sugars are attached. These include providing the basis for rigid conformations and for protein stability. Clustering of O-glycans in Ser/Thr(/Pro)-rich domains allows glycan determinants such as sialyl Lewis X to be presented as multivalent ligands, essential for functional recognition. An additional level of regulation, imposed by exon shuffling and alternative splicing of mRNA, results in the expression of proteins that differ only by the presence or absence of Ser/Thr(/Pro)-rich domains. These domains may serve as protease-resistant spacers in cell surface glycoproteins. Further biological roles for O-glycosylation discussed include the role of isolated mucin-type O-glycans in recognition events (e.g., during fertilization and in the immune response) and in the modulation of the activity of enzymes and signaling molecules. In some cases, the O-linked oligosaccharides are necessary for glycoprotein expression and processing. In contrast to the more common mucin-type O-glycosylation, some specific types of O-glycosylation, such as the O-linked attachment of fucose and glucose, are sequon dependent. The reversible attachment of O-linked GlcNAc to cytoplasmic and nuclear proteins is thought to play a regulatory role in protein function. The recent development of novel technologies for glycan analysis promises to yield new insights in the factors that determine site occupancy, structure-function relationship, and the contribution of O-linked sugars to physiological and pathological processes. These include diseases where one or more of the O-glycan processing enzymes are aberrantly regulated or deficient, such as HEMPAS and cancer.

Expression of mucin-associated tumor antigens is altered by cell density

Mucin-associated sialylated Lewis antigens are implicated in tumor cell metastasis and are used in several tests for pancreatic cancer. Despite their clinical importance, little is known about the structures of the oligosaccharides of pancreatic cancer mucins or about the regulation of their synthesis or of the synthesis of their protein cores. In this study, we examined the effects of culture at high cell density on the expression of these antigens in the SW1990 human pancreatic cancer cell line. Mucins from cells that were 2.5 weeks post-confluent had increased expression of sialyl-Lewis(a) and Lewis(x) antigens but reduced expression of the DU-PAN-2 antigen (NeuAc alpha2,3Galbeta1,3GlcNAc-Gal-R) when compared to mucins from 1 day post-confluent cells. Sialyl-Lewis antigens differ from the DU-PAN-2 antigen by the presence of an additional fucose. Mucins from 2.5-week cells also had increased binding to lectins specific for fucose, such as AAL and UEAI, with no apparent change in the binding of lectins specific for sialic acids. Metabolically radiolabeled O-linked oligosaccharides with sialyl-Lewis(a) antigenic reactivity eluted from Bio-Gel P-10 in the region of sialylated and sulfated oligosaccharides. Oligosaccharides eluted from QAE-Sephadex (2 mM Tris base) in a pattern suggesting the presence of 1, 2 and 3 or more negative charges per oligosaccharide. Even after desialylation and desulfation, oligosaccharides eluted from Bio-Gel P-10 with apparent molecular sizes greater than glucose oligomers of 12 units. Culture of SW 1990 cells at high density also increased the steady-state levels of mRNA for mucins MUC1, 2, 4, 5 and 6. In summary, after prolonged culture at high cell density, SW1990 cells have qualitative changes in their oligosaccharides that may be due to up-regulation of fucosyltransferases.

Mucins secreted by cell lines derived from colorectal mucinous carcinoma and adenocarcinoma

Mucinous (colloid) carcinoma and well- to moderately-differentiated adenocarcinoma of the colon differ in the pattern and the amount of mucin secretion and perhaps in their behaviour and clinical outcome. To ascertain why these differences exist and to elucidate the mechanisms of tumour progression, we examined two model human cell lines derived from colorectal mucinous carcinoma (C1a) and moderately differentiated adenocarcinoma (HM3) which show typical pathological and mucin staining patterns of the respective type of carcinomas to nude mouse tumour xenografts. Specifically, we sought to determine if there were quantitative and qualitative differences in mucin synthesis, in mucin gene expression and in biological properties between the two model cell lines. Northern blot analysis showed that MUC2 mRNA levels were significantly higher in C1a cells compared with HM3 cells, while those of MUC3, -5 and -6 mRNA were lower. C1a cells secreted approximately five times more radiolabelled apomucin and 1.5 times more glycosylated apomucin than HM3 cells. When the carbohydrate side-chain length of secreted mucins by these cell lines were examined by beta-elimination followed by P4 column chromatography, C1a mucins had mostly short carbohydrate side-chains, while HM3 cells had predominantly longer side-chains. Western blot analysis of the cell homogenate showed higher expression of MUC2 apomucin and mucin-associated carbohydrate antigens, such as T, Tn and sialyl Tn, with decreased sialyl Le(x) expression in C1a cells compared with HM3. Immunohistochemical analysis of 35 colorectal adenocarcinoma and 25 mucinous colorectal carcinoma tissues also demonstrated increased MUC2 apomucin, T, Tn and sialyl Tn antigens in the mucinous cancer specimens. Examination of the biological properties of these cell lines showed that C1a cells had significantly higher in vitro invasive activity in assays of invasion and collagenase activity and significantly lower E-selectin binding and liver colonisation activities in nude mice. These results indicate that colorectal mucinous carcinoma cells differ considerably from colorectal adenocarcinoma cells, both qualitatively and quantitatively, in the pattern of mucin gene expression and in the synthesis and secretion of mucin. In addition, biological studies showed that mucinous carcinoma cells have a greater degree of invasiveness, but less liver colonising activity. These results suggest that the biological and mucin characteristics of mucinous carcinoma cells contribute to extensive local invasion through tissue stroma as the predominant mechanism of tumour progression, while the biological and mucin characteristics of well- to moderately-differentiated colorectal adenocarcinoma contribute to progression via distant metastasis formation.

Mucin glycoproteins in neoplasia

Mucins are high molecular weight glycoproteins that are heavily glycosylated with many oligosaccharide side chains linked O-glycosidically to the protein backbone. With the recent application of molecular biological methods, the structures of apomucins and regulation of mucin genes are beginning to be understood. At least nine human mucin genes have been identified to date. Although a complete protein sequence is known for only three human mucins (MUC1, MUC2, and MUC7), common motifs have been identified in many mucins. The pattern of tissue and cell-specific expression of these mucin genes are emerging, suggesting a distinct role for each member of this diverse mucin gene family. In epithelial cancers, many of the phenotypic markers for pre-malignant and malignant cells have been found on the carbohydrate and peptide moieties of mucin glycoproteins. The expression of carbohydrate antigens appears to be due to modification of peripheral carbohydrate structures and the exposure of inner core region carbohydrates. The expression of some of the sialylated carbohydrate antigens appears to correlate with poor prognosis and increased metastatic potential in some cancers. The exposure of peptide backbone structures of mucin glycoproteins in malignancies appears to be due to abnormal glycosylation during biosynthesis. Dysregulation of tissue and cell-specific expression of mucin genes also occurs in epithelial cancers. At present, the role of mucin glycoproteins in various stages of epithelial cell carcinogenesis (including the preneoplastic state and metastasis), in cancer diagnosis and immunotherapy is under investigation.

Establishment of two new scirrhous gastric cancer cell lines: analysis of factors associated with disseminated metastasis

Determination of the differences between cell lines which are derived from a primary tumour and a disseminated metastatic lesion from the same patient may aid in elucidating the factors associated with disseminated metastases. We report on the establishment and characterisation of two new scirrhous gastric cancer cell lines, designated OCUM-2M and OCUM-2D, derived from a 49-year-old female. OCUM-2M was derived from a primary gastric tumour, and OCUM-2D was derived from a sample of disseminated metastasis. The two cell lines were derived from the same patient. We investigated biological differences between the two cell lines to study mechanisms involved in disseminated metastasis. The growth activity of OCUM-2D cells as determined by doubling time and tumorigenicity was greater than that of OCUM-2M cells. The level of epidermal growth factor receptor (EGFR) expression in OCUM-2D cells was about twice that of OCUM-2M cells and the growth of OCUM-2D cells was stimulated more by epidermal growth factor (EGF) than that of OCUM-2M cells. The invasive activity of OCUM-2D cells was higher than that of OCUM-2M cells and was increased after addition of transforming growth factor-beta 1 (TGF-beta 1). An increase in the number of attached and spreading cells was found following the addition of 10 ng ml-1 TGF-beta 1. These findings suggest that high growth and invasive activity may play an important role in disseminated metastasis and that EGF and TGF-beta 1, which affect the growth and invasive activity of OCUM-2D cells, might be factors associated with metastasis in scirrhous gastric carcinoma. The two cell lines OCUM-2M and OCUM-2D should be beneficial for analysing mechanisms of tumour progression.

Transformation of human keratinocytes is characterized by quantitative and qualitative alterations of the T-16 antigen (Trop-2, MOv-16)

The regulation of synthesis and post-translational processing of the T-16 antigen, a human cell-surface glycoprotein of 50 to 60 kDa, was investigated in normal and transformed human keratinocytes in vitro. Normal keratinocytes of interfollicular and follicular origin were compared with squamous-cell-carcinoma lines, spontaneously immortalized keratinocytes, and SV-40 transformed keratinocytes. FACS analysis and radio-immunoprecipitation showed that the synthesis and expression of T-16 was 3- to 4-fold higher in transformed keratinocytes than in their normal counterparts. In normal keratinocytes, no quantitative differences were observed among freshly prepared cells, primary cultures and sub-cultures. In SDS-PAGE, a single broad band at 50 to 60 kDa was observed in normal keratinocytes, whereas 2 bands at 42 and 45 to 55 kDa were detected after transformation. Tunicamycin treatment of living cells and glycosidase digestion of immunopurified T-16 antigen revealed this molecular heterogeneity to be due to different N-glycosylation in normal and transformed keratinocytes. In pulse-chase experiments, 2 distinct precursor proteins at 38 and 42 kDa were detected in transformed keratinocytes, whereas in normal cells the 38-kDa signal was dramatically decreased. These findings indicate that quantitative and qualitative changes of T-16 mark the transformation process of human keratinocytes, showing similar post-translational alterations in all transformed populations investigated.

E-selectin binding by pancreatic tumor cells is inhibited by cancer sera

Tumor cells interact with endothelial cells during both intra- and extravasation. Understanding how these interactions are modulated could lead to the development of ways to alter the metastatic potential of tumor cells. Three pancreatic cancer cell lines, SW1990, CAPAN-2 and PANC-I, were examined for their ability to bind to the endothelial cell adhesion molecule E-selectin (ELAM-1). SW1990 cells exhibited highest binding, highest surface expression of the carbohydrate antigens sialylated Lewis(a) (sLe(a)) and sialylated Lewis(x) (sLe(x)) and released the most high m.w. sLe(a) and sLe(x) antigens. Expression of sLe(a) and sLe(x) antigens and binding to E-selectin were reduced by pre-treatment of SW1990 cells with the O-linked glycosylation inhibitor benzyl-alpha-GalNAc but not with the N-linked glycosylation inhibitor tunicamycin. Expression of peptide epitopes associated with MUC1 apomucins was increased by benzyl-alpha-GalNAc. Cell binding was greatly reduced by mucins purified from SW1990 xenografts and by an antibody against sLe(a). An antibody against sLe(x) had a much less marked effect. Sera from pancreatic cancer patients reduced SW1990 cell binding to E-selectin but sera from normals did not. The degree of inhibition was related to the sLe(x) level in the sample. When cancer serum was separated by column chromatography on Sephacryl S-400, the void volume fractions contained most of the sLe(a) and sLe(x) antigens and most of the inhibitory activity to E-selectin binding. Differences in the relative availability of sLe(a) and sLe(x) ligands on serum molecules and on the SW1990 cell surface may account for the differences between antibody and serum inhibition results. Thus SW1990 cell adhesion to E-selectin is mediated by ligands on mucinous glycoproteins, and adhesion can be inhibited by mucins, high blood levels of sLe(x) and reduction of cellular O-linked glycosylation.